The Spin Cycle: PBOT Reports Auto Travel On Bridges Down, Using Old Numbers

Two months later than expected, Portland's Bureau of Transportation today released its 2009 Bicycle Countshowing that the number of bike trips in Portland dropped 5 percent compared with 2008. That's the first such year-to-year drop since 1995.

Yesterday, we revealed another element to this decline in ridership: PBOT data shows auto traffic on Portland's four bike-friendly bridges (Broadway, Steel, Burnside and Hawthorne) has also declined -- by 10 percent. Meanwhile, bike ridership across those four bridges fell 6 percent.

That apples-to-oranges comparison carries a huge caveat, which PBOT reveals in a footnote on page 2 of the report:

Annual automobile counts are not typically conducted on the four bridges. However, in 2009 PBOT did conduct counts on the four bicycle-friendly bridges. Those counts showed an overall ten percent decrease from 2005, when the last counts were taken on all but the Steel Bridge.

Before 2009, the last count of cars on the Steel Bridge took place in 2001.

What's remarkable about the auto counts on bridges is that the number of car trips in and out of downtown Portland, according to PBOT's data, has fluctuated since 1991 but has generally declined since around 2000.

Having not measured car travel for several years, it's not possible to say by how much car travel across bridges decreased in 2009 compared with 2008.

On page 5 of the report the city also uses car counts at a number of Portland intersections to buttress the assertion that auto travel dipped in 2009. But it appears precise comparisons to 2008 are not possible there either; PBOT has car counts for 2008 for only two out of the 26 intersections listed in the report.